1. Field of the Invention
The present invention is directed to a method for monitoring a process facility, such as an electrical power generating plant and, more particularly, to such a method in which sequential conditions which are associated with specific steps of a plant procedure are selectively transformed into constraining conditions which are applicable to several steps of that procedure.
2. Description of the Related Art
In recent years, there have been a variety of systems developed for monitoring the operation of process facilities, such as industrial plants of many types, including both nuclear powered and fossil fueled electrical power generating plants. Many of these systems use artificial intelligence, e.g., expert systems, or other types of computer programs operating on data provided by sensors throughout the plant. One example of such a system is disclosed in U.S. Pat. Nos. 4,803,039 and 4,815,014 which are assigned to the assignee of this application and which are incorporated herein by reference. These patents disclose a system executing a FORTRAN program which includes program code for all of the written procedures for a particular type of operation of a plant, for example, the emergency operating procedures (EOP). As disclosed in allowed U.S. patent application Ser. No. 07/307,831, incorporated herein by reference, this system may be used to monitor the execution of procedures using three classes of conditions which typically exist during execution of a procedure for operating the plant. The first class consists of terminal conditions which include both initial conditions that must be satisfied prior to beginning a procedure and final conditions that determine completion of a procedure. The second class consists of sequential conditions, each of which corresponds to a particular step in the procedure and is intended to be met prior to completing the corresponding step. Finally, there are constraining conditions which remain in effect for several steps. While all of these types of conditions are not always clearly defined in the written procedures, computerization of the procedures requires that the conditions be defined rigorously.
Successful execution of such procedures hinges on the ability of either the operator to guide the system or the system to pace itself through the prespecified sequence of plant state changes defined in the procedure. However, in conventional systems, once a sequential condition has been met, the existing systems do not continue to check to ensure that the sequential condition is maintained. Hence, later during execution of the procedure, the monitoring system would be unaware of any changes in the plant which affect a previously established condition and thus the operator would not be alerted by the system of the non-existence of an assumed condition.
On the other hand, constraining conditions are based on precautions, limitations, notes, etc. in written procedures. Constraining conditions are assumed to be passive unless violated. Hence, typically, the operator is not informed about constraining conditions, unless a violation has occurred or is impending. If such an event occurs, conventional systems alert the operator, indicate the problem by text or graphics and require acknowledgement that the operator has become aware of the situation. All applicable constraining conditions are tested in each pass through a continuously executed loop in a computer program. Typically, the loop is interrupted only from the time a violation is detected until the operator's acknowledgement is received. A complete loop is executed periodically with a frequency that depends upon the capabilities of the system and the type of operation being monitored.
In a conventional system, due to the necessity to clearly encode all sequential and constraining conditions, the only way to have a particular condition included as a sequential condition in a particular step and thereafter monitored continuously is to include separate blocks of computer program code in both the sequential steps and in the set of constraining conditions. The constraining condition must become effective only after completion of the step in which the corresponding sequential condition appears. This requires careful verification of the computer program to ensure that the same condition is being tested at the appropriate times. In a computerized procedure for a complex process facility, such as a nuclear power plant, there may be tens of thousands of lines of code and verification is not a trivial task. Furthermore, there is no opportunity for an operator to select a sequential condition to be continually monitored after the sequential condition is met, based upon recent experiences in operating the plant.